Add SQL semantic search schema foundations

[Brendan Kowitz (brendankowitz)]

Description

Layer 1 of the SQL semantic-search stack; targets main.

• Add schema versions 117–119: embedding-model registry, native vector(1536) storage, vector TVP, atomic merge/reindex/delete support, and dormant source-refresh procedures.
• Keep runtime indexing, Foundry calls, search operations, and refresh workers out of this layer.
• Build against released Microsoft.Health packages using a narrow local VectorColumn descriptor; no local-preview packages or machine-specific feeds.
• Preserve supported older-schema callers, omitted-TVP legacy calls against schema 119, migration reapplication, and snapshot/diff equivalence. Explicitly reject database engines that lack the required native-vector platform support.

The next PR adds the direct-text SearchParameter/Foundry MVP. Binary/PDF, evidence, chaining, and the Patient operation remain in the unpublished third layer.

Substantial extracted code retains original author Anna Gornyitzki; compatibility adaptations are separate commits. Source implementation: #5780. Architecture: docs/arch/adr-2608-sql-semantic-search.md.

Related issues

Extracted from #5780; this PR does not close a separate issue.

Testing

• SQL project build succeeded with released packages.
• SQL unit suite: 1,045 passed.
• Isolated schema/compatibility integration coverage: 4 passed, including nonempty pre-117 caller writes against schema 119 and schema snapshot/diff equivalence.
• SQL engine guard exercised against SQL Server 2025 and SQL Server 2019 LocalDB.

FHIR Team Checklist

• Update the title of the PR to be succinct and less than 65 characters
• Add a milestone to the PR for the sprint that it is merged (i.e. add S47)
• Tag the PR with the type of update: Bug, Build, Dependencies, Enhancement, New-Feature or Documentation
• Tag the PR with Open source, Azure API for FHIR (CosmosDB or common code) or Azure Healthcare APIs (SQL or common code) to specify where this change is intended to be released.
• Tag the PR with Schema Version backward compatible or Schema Version backward incompatible or Schema Version unchanged if this adds or updates Sql script which is/is not backward compatible with the code.
• When changing or adding behavior, if your code modifies the system design or changes design assumptions, please create and include an ADR.
• CI is green before merge
• Review squash-merge requirements

Semver Change (docs)

Breaking — applying the new native-vector schema requires SQL Server 2025 or a supported Azure SQL platform; legacy application procedure callers remain compatible.

[Codecov Comments Bot (codecov-commenter)]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.87%. Comparing base (ef77cdc) to head (4a3b2c9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5802      +/-   ##
==========================================
+ Coverage   78.29%   78.87%   +0.58%     
==========================================
  Files        1016     1017       +1     
  Lines       36911    36912       +1     
  Branches     5617     5616       -1     
==========================================
+ Hits        28898    29114     +216     
+ Misses       6635     6410     -225     
- Partials     1378     1388      +10     

see 15 files with indirect coverage changes

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